In humans and non-human primates, the vast majority of maternal-fetal exchanges are mediated by the placenta. It is, therefore, of fundamental importance to our understanding of fetal nutritional and neonatal health problems to ascertain the mechanisms by which the placenta selectively absorbs substances from the maternal blood and transports them to the fetus. The major components separating the maternal and fetal bloodstreams are: 1) syncytial trophoblast 2) a basal lamina and 3) fetal capillaries. The experiments encompassed in this proposal will examine various structural and functional aspects of each of these components, especially as they relate to absorption and permeability. Receptor-mediated endocytosis is one important mechanism by which cells, including trophoblast, take up macromolecules from their environment. This process will be examined in detail by combined ultrastructural and biochemical methods in order to quantitatively detemine the manner in which various ligands interact with trophoblast, and ultrastructurally and immunocytochemically to determine the intracellular pathways followed by ligands and their receptors. The ligands selected include IgG, because of its importance in providing passive immunity to the fetus, LDL because of its importance as a precursor for hormone synthesis and transferrin because of its role in iron transport tothe fetus. Because of the potentially important role of the cytoskeleton in many cellular functions, including endocytosis, other studies will determine the composition and localization of major cytoskeletal proteins in human placenta using immunofluorescent and ultrastructural immunocytochemical methods. In addition to macromolecules, the transport of ions to the developing fetus is another vitally important placental function. In order to better understand the subcellular structures associated with active ion transport by placenta we will localize Na+, K+ ATPase, Ca++ ATPase, and Ca++ in human placenta using ultratructural cytochemistry. The structural and functional basis of trophoblast and amnion basal lamina permeability will be studied. Isolated basal laminas will be exposed to tracer proteins with and without selective removal of basal lamina will be exposed to tracer proteins with and without selective removal of basal lamina glycosaminoglycans, particularly heparan sulfate to determine if these components influence permeability. Finally, the three-dimensional arrangement of the fetal capillary bed in terminal and intermediate human and non-human primate placental villi will be examined in order to determine how their structural organization may affect maternal-fetal exchange.